The present application is concerned with coding concepts allowing efficient multi-view/layer coding such as multi-view picture/video coding.
In Scalable Video Coding (SVC) the coded picture buffer (CPB) operates on complete access units (AUs). All Network Abstraction Layer Units (NALUs) of one AU are removed from the Coded Picture Buffer (CPB) at the same time instant. An AU contains the packets (i.e. NALUs) of all layers.
In the HEVC base specification the concept of decoding units (DU) is added compared to H.264/AVC. A DU is a group of NAL units at consecutive positions in the bitstream. In a single layer video bitstream all these NAL units belong to the same layer, i.e. that so called base layer.
The HEVC base specification contains the tools needed to allow decoding of bitstreams with ultra-low delay, i.e. through CPB operation on DU level and CPB timing information with DU granularity as opposed to CPB operation on AU level as in H.264/AVC. Thus, a device can operate on sub-portions of pictures in order to reduce occurring processing delays.
For similar ultra-low delay operations in the multi-layer SHVC, MV-HEVC and 3D-HEVC extensions of HEVC, CPB operations on DU level across layers need to be defined accordingly. Particularly, a bitstream in which the DUs of an AU with several layers or views are interleaved across layers is necessitated, i.e. DUs of layer m of a given AU may follow DUs of layer (m+1) of the same AU in such an ultra-low delay enabled multi-layer bitstream as long as there are no dependencies on the DUs following in bitstream order.
The ultra-low delay operation necessitates modifications of the CPB operation for a multi-layer decoder compared to the SVC and MVC extension of H.264/AVC that work based on AUs. An ultra-low delay decoder can make use of additional timing information, e.g. provided through SEI messages.
Some implementations of a multi-layer decoder may advantageously use a layer-wise decoding (and CPB operation either on DU or AU level), i.e. decoding of layer m prior to decoding of layer m+1, which would effectively prohibit any multi-layer ultra-low delay applications with SHVC, MV-HEVC and 3D-HEVC, unless new mechanisms are provided.
Currently, the HEVC base spec contains two decoding operation modes:                access unit (AU) based decoding: all decoding units of an access unit are removed from the CPB at the same time        decoding unit (DU) based decoding: each decoding unit has an own CPB removal time        
Nevertheless, it would be more favorable to have concepts at hand which further improve multi-view/layer coding concepts.
Accordingly, it is the object of the present invention to provide concepts which further improve multi-view/layer coding concepts. In particular, it is the object of the present invention to provide a possibility to enable low end-to-end delay without, however, giving up at least one fallback position for decoders not able to deal with, or deciding not to use, the low delay concept.